[rizzom5000]

I think I'm with you on this one. Crappy code can still get a lot of stars/forks and great code can pretty much get ignored if it's not the flavor of the month with the majority bandwagon. I think Github is great if you want to look at someone's code, but being able to successfully answer questions, while more academic than utilitarian, in general identifies those with a deep and thorough understanding of the technology. SO gets gamed though.

Ultimately, I suppose that either are a good bet if you're looking for someone who stands out in a certain way. In both places you should vet the quality of the code or quality of the answers. And if you're the type of employer who uses these as metrics for rating candidates, then I think you should also probably give your employees time to work on their Github projects/SO profiles (I didn't intend the irony there, but it's there all the same).